The invention relates to a belt grinder or band sander. DE 37 15 292 A1 discloses a band sander of this type in which the motor shaft and the driven band roller each support a belt pulley. The distance between the belt pulleys is fixed by design. However, for this reason the tension of the belt tightened over the belt pulleys cannot be adjusted subsequently. Excessive tension in the belt reduces the performance of the band sander and can lead to premature wear at the bearings and belt. Belts with insufficient tension also wear out faster, result in slippage and frequently cause disturbingly loud operating noise.